1. Field of the Invention
The present invention generally relates to grayscale binning and, more particularly, to a method of grayscale image segmentation used for low contrast or busy image pattern recognition.
2. Background Description
Traditional binary image segmentation methods do not work on complex grayscale images with low contrast. An example of this problem is observed in applying segmentation techniques to postal bundle markers, pre-sort labels and other non-address postal glyphs, or address labels.
Being more specific, the small bundle markers (pre-sort labels) have a colored background which typically do not have enough contrast against a parcel background to allow effective binarization. The limited contrast between the pattern and the background results in critical information loss in the form of partial bundle mark pattern after a binarization algorithm is applied. In turn, this critical information loss may result in the mail having to be manually read and hence pre-sorted thereby resulting in added expense and time.
In order to segment and locate bundle marks on postal applications, it is thus necessary to use grayscale or color image in the segmentation process. The techniques applied to grayscale segmentation traditionally include region growing or split or merge or watershed methods. Additional segmentation methods may include boundary or edge detection, level-sets, as well as multi-resolution techniques such as, for example, wavelet, Gabor or Steerable filter, or threshold methods aimed at binary images. However, due to timing constraints and lack of contrast on “busy” magazine or parcel images, these techniques are not effective in locating the search targets within the timing budget.
The ability to identify the pre-sort label on a parcel representing different mail classes is necessary for parcel programs. On certain packages, the white address label in different sizes and shapes has relatively low contrast against a light brown package, for example. Due to this low contrast, it is very difficult to locate the pre-sort label or the white address label on the noisy binary image derived using the traditional threshold methods. It is also difficult to locate Royal mail glyphs in threshold binarized image. It is for these and other reasons that to locate the pre-sorting of mail with low contrast labels is difficult, time consuming and relatively inaccurate.